Experimental and theoretical studies of redox reactions of o-chloranil in aqueous solution

The redox potential of flavin derivatives as a mediator in biosensors

The two-electron reduction potential for a set of 393 flavin derivatives is presented in this article. These derivatives are substituted flavin on carbon 6, 7, 8, and 9 by coinage transition metals (Cu, Ag, and Au) and conjugated double bond hydrocarbons; and both groups are examined with and without functional groups such as OH, Cl, CH₃, COOH, and NO₂. In order to show the validity of the results, the reduction potential of human life molecules, which have experimental values, such as flavin adenine dinucleotide (FAD) and riboflavin (vitamin B₂) is calculated. The experimental value for FAD is - 0.22 V, while the obtained theoretical value is - 0.21 V, and the corresponding values for riboflavin are - 0.18 and - 0.19 V, respectively. Theoretical calculations have been carried out by DFT procedure with a 6-31+G** basis set and BLYP xc-functional for coinage transition metals substitution, and MPW1PW9 xc-functionals for conjugated double bond hydrocarbon substitution. Both xc-functionals are chosen by the DFT calibration procedure.

One-Electron Reduction Potentials: Calibration of Theoretical Protocols for Morita⁻Baylis⁻Hillman Nitroaromatic Compounds in Aprotic Media

Nitroaromatic compounds—adducts of Morita–Baylis–Hillman (MBHA) reaction—have been applied in the treatment of malaria, leishmaniasis, and Chagas disease. The biological activity of these compounds is directly related to chemical reactivity in the environment, chemical structure of the compound, and reduction of the nitro group. Because of the last aspect, electrochemical methods are used to simulate the pharmacological activity of nitroaromatic compounds. In particular, previous studies have shown a correlation between the one-electron reduction potentials in aprotic medium (estimated by cyclic voltammetry) and antileishmanial activities (measured by the IC₅₀) for a series of twelve MBHA. In the present work, two different computational protocols were calibrated to simulate the reduction potentials for this series of molecules with the aim of supporting the molecular modeling of new pharmacological compounds from the prediction of their reduction potentials. The results showed that it was possible to predict the experimental reduction potential for the calibration set with mean absolute errors of less than 25 mV (about 0.6 kcal·mol⁻¹).

Metal Free Reversible-Deactivation Radical Polymerizations: Advances, Challenges, and Opportunities

A considerable amount of the worldwide industrial production of synthetic polymers is currently based on radical polymerization methods. The steadily increasing demand on high performance plastics and tailored polymers which serve specialized applications is driven by the development of new techniques to enable control of polymerization reactions on a molecular level. Contrary to conventional radical polymerization, reversible-deactivation radical polymerization (RDRP) techniques provide the possibility to prepare polymers with well-defined structures and functionalities. The review provides a comprehensive summary over the development of the three most important RDRP methods, which are nitroxide mediated radical polymerization, atom transfer radical polymerization and reversible addition fragmentation chain transfer polymerization. The focus thereby is set on the newest developments in transition metal free systems, which allow using these techniques for biological or biomedical applications. After each section selected examples from materials synthesis and application to biomedical materials are summarized.

A DFT study on the reaction mechanism between tetrachloro-o-benzoquinone and H2O2 and an alternative reaction approach to produce the hydroxyl radical

The reaction mechanism between tetrachloro-o-benzoquinone and H₂O₂ was studied theoretically and an alternative approach to produce the hydroxyl radical was proposed.

Insights into the one-electron reduction behavior of tetrachloro-o-benzoquinone: a DFT and molecular dynamics study

One-electron reduction behavior of tetrachloro-o-benzoquinone has been studied theoretically and it is a good electron acceptor in various media.

Theoretical insights into the reaction mechanism between tetrachloro-o-benzoquinone and N-methyl benzohydroxamic acid

The reaction mechanism between tetrachloro-o-benzoquinone and N-methyl benzohydroxamic acid has been clarified theoretically.

Oxidovanadium(IV/V) complexes as new redox mediators in dye-sensitized solar cells: a combined experimental and theoretical study

Corrosiveness is one of the main drawbacks of using the iodide/triiodide redox couple in dye-sensitized solar cells (DSSCs). Alternative redox couples including transition metal complexes have been investigated where surprisingly high efficiencies for the conversion of solar to electrical energy have been achieved. In this paper, we examined the development of a DSSC using an electrolyte based on square pyramidal oxidovanadium(IV/V) complexes. The oxidovanadium(IV) complex (Ph4P)2[V(IV)O(hybeb)] was combined with its oxidized analogue (Ph4P)[V(V)O(hybeb)] {where hybeb(4-) is the tetradentate diamidodiphenolate ligand [1-(2-hydroxybenzamido)-2-(2-pyridinecarboxamido)benzenato}and applied as a redox couple in the electrolyte of DSSCs. The complexes exhibit large electron exchange and transfer rates, which are evident from electron paramagnetic resonance spectroscopy and electrochemistry, rendering the oxidovanadium(IV/V) compounds suitable for redox mediators in DSSCs. The very large self-exchange rate constant offered an insight into the mechanism of the exchange reaction most likely mediated through an outer-sphere exchange mechanism. The [V(IV)O(hybeb)](2-)/[V(V)O(hybeb)](-) redox potential and the energy of highest occupied molecular orbital (HOMO) of the sensitizing dye N719 and the HOMO of [V(IV)O(hybeb)](2-) were calculated by means of density functional theory electronic structure calculation methods. The complexes were applied as a new redox mediator in DSSCs, while the cell performance was studied in terms of the concentration of the reduced and oxidized form of the complexes. These studies were performed with the commercial Ru-based sensitizer N719 absorbed on a TiO2 semiconducting film in the DSSC. Maximum energy conversion efficiencies of 2% at simulated solar light (AM 1.5; 1000 W m(-2)) with an open circuit voltage of 660 mV, a short-circuit current of 5.2 mA cm(-2), and a fill factor of 0.58 were recorded without the presence of any additives in the electrolyte.

Computational electrochemistry: prediction of liquid-phase reduction potentials

This article reviews recent developments and applications in the area of computational electrochemistry. Our focus is on predicting the reduction potentials of electron transfer and other electrochemical reactions and half-reactions in both aqueous and nonaqueous solutions. Topics covered include various computational protocols that combine quantum mechanical electronic structure methods (such as density functional theory) with implicit-solvent models, explicit-solvent protocols that employ Monte Carlo or molecular dynamics simulations (for example, Car-Parrinello molecular dynamics using the grand canonical ensemble formalism), and the Marcus theory of electronic charge transfer. We also review computational approaches based on empirical relationships between molecular and electronic structure and electron transfer reactivity. The scope of the implicit-solvent protocols is emphasized, and the present status of the theory and future directions are outlined.

Electrooxidation of homogentisic acid in aqueous and mixed solvent solutions: experimental and theoretical studies

Electrochemical behavior of homogentisic acid (HGA) has been studied in both aqueous and mixed solvent solution of water-acetonitrile. Physicochemical parameters of the electrochemical reaction of HGA in these solutions are obtained experimentally by cyclic voltammetry method and are also calculated theoretically using accurate ab initio calculations (G3MP2//B3LYP). Solvation energies are calculated using the available solvation model of CPCM. The pH dependence of the redox activity of HGA in aqueous and the mixture solutions at different temperatures was used for the experimental determination of the standard reduction potential and changes of entropy, enthalpy, and Gibbs free energy for the studied reaction. The experimental standard redox potential of the compound in aqueous solution was obtained to be 0.636 V versus the standard hydrogen electrode. There is a good agreement between the theoretical and experimental values (0.702 and 0.636 V) for the standard electrode potential of HGA. The changes of thermodynamic functions of solvation are also calculated from the differences between the solution-phase experimental values and the gas-phase theoretical values. Finally, using the value of solvation energy of HGA in water and acetonitrile solvents which calculated by the CPCM model of energy, we proposed an equation for calculating the standard redox potential of HGA in mixture solution of water and acetonitrile. A good agreement between the result of electrode potential calculated by the proposed equation and the experimental value confirms the validity of the theoretical models used here and the accuracy of experimental methods.

Thermodynamic parameters of electrochemical oxidation of L-DOPA: experimental and theoretical studies

Electrode potential and thermodynamic parameters of the electrochemical reaction of L-DOPA in aqueous solution are obtained experimentally by cyclic voltammetry method and also calculated theoretically using accurate ab initio calculations (G3MP2//B3LYP) along with the available solvation model of CPCM. The pH dependence of the redox activity of L-DOPA in aqueous solution at temperatures in the range of 10-30 °C was used for the experimental determination of the standard reduction potential, changes of entropy, enthalpy, and Gibbs free energy for the studied reaction. The experimental formal redox potential of the two-proton-two-electron reduction process was obtained to be 0.745 V versus standard hydrogen electrode (SHE). The theoretical and experimental values (0.728 and 0.745 V) for the standard electrode potential of L-DOPA are in agreement with each other. The difference between the peak potential of the L-DOPA and the products, which are produced by chemical reactions, has been measured experimentally and also calculated theoretically. There is also an agreement between experimental and theoretical potential difference. Also in this work, the changes of thermodynamic functions of solvation are calculated from the differences between the solution-phase experimental values and the gas-phase theoretical values.

Theoretical Study of the Oxidation Mechanism of Hematoxylin in Aqueous Solution

The oxidation of the two catechol rings A and B in the chemical structure of hematoxylin in aqueous solution has been studied theoretically in order to identify the mechanism of oxidation. In a recent experimental study, the oxidation mechanism of hematoxylin was designated an ErCiEr process in which an irreversible chemical reaction (Ci) followed the reversible chemical electrochemical oxidation (Er) of the catechol unit connected to the six-membered ring of the molecule (ring A). The theoretical results presented herein indicate that the electrochemical oxidation of ring B is actually slightly more favoured than ring A, although the potential separation is so small that they were unable to be distinguished in the experimental study. We therefore suggest that the most likely mechanism is ErErCiEr, in which two reversible electrochemical oxidation reactions (Er) occur preceding the irreversible chemical reaction (Ci), though we cannot rule out a contribution from ErCiEr. The calculated oxidation potential (0.719 V v. standard hydrogen electrode) is in close accord with the experimental value (0.759 V v. standard hydrogen electrode). The deprotonation of five hydroxyl groups of hematoxylin in aqueous solution is also studied and the order of acidic strength of these groups has been identified.

Benchmark Calculations of Absolute Reduction Potential of Ferricinium/Ferrocene Couple in Nonaqueous Solutions

High-level ab initio molecular orbital theory is used to obtain benchmark values for the ferricenium/ferrocene (Fc(+)/Fc) couple, the IUPAC recommended reference electrode for nonaqueous solution. The gas-phase ionization energy of ferrocene is calculated using the high-level composite method, G3(MP2)-RAD, and two higher-level variants of this method. These latter methods incorporate corrections for core correlation and, in the case of the highest level considered, use (RO)CCSD(T)/6-311+G(d,p) in place of (RO)CCSD(T)/6-31G(d) as the base level of theory. All methods provide good agreement with one another and the corresponding experimental values. Solvation energies have been calculated using PCM, CPCM, SMD, and COSMO-RS. Using G3(MP2)-RAD-Full-TZ gas-phase energies and COSMO-RS solvation energies, the absolute redox potentials of the Fc(+)/Fc couple have been calculated as 4.988, 4.927, and 5.043 V in acetonitrile, 1,2-dichloroethane, and dimethylsulfoxide solutions, respectively.